Prolapse into the bile duct and expansive growth is characteristic behavior of mucinous cystic neoplasm of the liver: report of two cases and review of the literature.

Mucinous cystic neoplasm of the liver (MCN-L) is a very rare tumor whose detailed behavior is still unknown. We describe two cases of MCN-L that exhibited extremely interesting growth patterns, and discuss the characteristics of MCN-Ls. Both cases exhibited MCN-L that originated from the left hepatic lobe (Segment 4) and then prolapsed into the left hepatic duct and common bile duct, resulting in obstructive jaundice due to expansive growth. Endoscopic retrograde cholangiopancreatographies showed the characteristic oval-shaped filling defects in the bile ducts. Endoscopic ultrasound and intraductal ultrasound were useful for differentiating the tumors from stones, since multiple septal formations were observed inside the tumors. A literature search revealed that, over the past 10 years, 15 cases of MCN-L (biliary cystadenomas with ovarian-like stroma) that showed expansive growth in the bile duct had been reported. Prolapse into the bile duct and expansive growth appear to be characteristic behavior of MCN-L. In the future, additional data on more cases needs to be collected to further elucidate MCN-L pathophysiology.